Stab-type couplings for connecting smooth walled non-metallic pipes are known, for example, in U.S. Pat. No. 4,229,025 which is incorporated herein by reference.
These couplings are particularly useful for connecting lengths of plastic pipe, such as plastic pipe used in transmission of natural gas. These stab-type couplings include a tapered, non-metallic coupling body surrounding a coupler assemble which receives the end of a plastic pipe. The coupler assembly inside the coupling body includes a hollow insert tube which fits inside the end of the pipe and a retaining collet which grips an exterior surface of the pipe. The collet is a generally tapered member having a series of circumferential interior teeth for gripping the pipe. The collet also includes a plurality of longitudinally extending recesses which allow the collet to expand and contract as necessary to receive and hold the pipe. The coupler assembly also includes various spacing and sealing members within the coupler body.
The coupler body of the known stab-type coupling is generally attached at one end to another member such as a male or female threaded member, a T-shaped or L-shaped member, or a second coupler body so that a pipe can be coupled to one or more other pipes or other members. A single coupler body of the type disclosed in the ""025 patent is shown in FIG. 1. In operation, a free end of a plastic pipe is pushed into the stab-type coupling from the right side of the coupling as shown in the FIGURE. Once the pipe is inserted, the collet prevents the pipe from being removed because attempted pull-out of the pipe will cause the collet to move to the right in the Figure engaging a tapered stainless steel back-up ring which is molded into the interior of the coupling body and causing the sharp interior teeth of the collet to grip the exterior of the pipe. Sealing of the pipe is actually performed by the sealing O-rings provided within the coupling.
The interior teeth of the collet have relatively sharp edges which bite into the pipe and do not allow it to be removed by pulling axially on the pipe. However, the collet having interior circumferential teeth will allow the pipe to be removed or loosened when the pipe is rotated within the collet achieving an unscrewing action.
For example, it has been found that the coupling described in the ""025 patent can become unscrewed from the coupling either intentionally or unintentionally by rotating the plastic pipe with respect to the collet and coupling body.
In order to prevent the possibility of unscrewing a plastic pipe from a stab-type coupling, a collet has been designed as shown in the drawings.
The present invention contemplates a new and improved stab-type coupling that overcomes the above-referenced problems and others and provides a simple, economical solution to these problems.
According to the present invention, there is provided a coupling that receives a non-metallic tube end. The coupling includes a body having an opening at one end that receives the tube end and a seal assembly received in the body that seals between the body and tube end. A collet disposed in the coupling body has an external tapered surface that engages a tapered wall of the coupling body cavity to resist pull-out forces. The collet further includes an inner toothed surface that grips the non-metallic tube end. A rotation prevention member, such as a longitudinal rib, extends inwardly from the collet and prevents relative rotation between the collet and tube.
According to another aspect of the invention, the collet is split by one or more slots that allow the collet to radially expand and contract. Edges of the split may be rounded to allow the collet to rotate relative to the coupling body.
A principal advantage of the invention is the ability to provide a stab-type coupling in which the tube end cannot be rotatably withdrawn.
Still another advantage of the invention resides in the ease with which the solution is accomplished.
Yet another advantage of the invention is associated with the smooth edges that allow the collet to rotate relative to the body.
Still other advantages and benefits of the invention will become apparent to others upon reading and understanding the following detailed description.